[PATCH v5 08/19] selftests/mm: add folio-order check for address ranges

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>

An mTHP collapse test needs to know that a range is backed by folios of the
target order, and that they sit where a collapse would put them.  Nothing
answers that today: is_backed_by_folio() classifies the folio behind a
single page, and check_huge_anon() reads smaps AnonHugePages, which only
accounts PMD mappings.

Add is_range_backed_by_order().  It requires every folio-sized, folio-
aligned part of the range to map one folio of that order, head to tail,
with the head at the start of the part.

A part backed by two smaller folios fails, and so does a folio mapped off
its natural alignment.  The mTHP cases need both to tell a collapsed range
from the one beside it.

Assisted-by: LLM
Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
---
 tools/testing/selftests/mm/vm_util.c | 47 ++++++++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h |  2 ++
 2 files changed, 49 insertions(+)

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 3ea42a7a2a3e..4947612e8b3d 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -552,6 +552,53 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 	return false;
 }
 
+/**
+ * is_range_backed_by_order() - check that a range is backed by @order folios
+ * @start: start of the range, a multiple of the folio size
+ * @len: length of the range in bytes, a multiple of the folio size
+ * @order: the folio order to check for
+ * @pagemap_fd: open /proc/<pid>/pagemap of the range's owner
+ * @kpageflags_fd: open /proc/kpageflags
+ *
+ * Every folio-sized, folio-aligned part of the range must map one folio of
+ * @order, head to tail, with the head at the start of the part.  A part
+ * backed by several smaller folios fails, and so does a folio mapped off
+ * its natural alignment.
+ *
+ * Returns: true if the whole range is backed that way, false otherwise.
+ */
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd)
+{
+	const unsigned long nr_pages = 1UL << order;
+	const size_t folio_size = nr_pages * psize();
+	char *vaddr;
+
+	if ((uintptr_t)start % folio_size || len % folio_size)
+		return false;
+
+	for (vaddr = start; vaddr < start + len; vaddr += folio_size) {
+		const unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+		unsigned long i;
+
+		/* Not present, or a tail page */
+		if (pfn == -1UL || pfn % nr_pages)
+			return false;
+
+		for (i = 1; i < nr_pages; i++) {
+			char *page = vaddr + i * psize();
+
+			if (pagemap_get_pfn(pagemap_fd, page) != pfn + i)
+				return false;
+		}
+
+		if (!is_backed_by_folio(vaddr, order, pagemap_fd, kpageflags_fd))
+			return false;
+	}
+
+	return true;
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 56a28ce7d029..e509fc4012a5 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -99,6 +99,8 @@ int gather_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
 bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 			int kpageflags_fd);
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.54.0